What are the differences in using POST and PUT methods when sending HTTP requests?

The POST and PUT methods in HTTP are used to send data to the server, but they have different semantic meanings and behaviors:

• POST — used to create a new resource. POST requests are not idempotent, meaning that repeated requests can lead to multiple resources being created. Typically, POST sends data to the server, and the server decides where and how to store the resource.

• PUT — used to create or replace a resource at a specific URI. PUT requests are idempotent: repeated requests with the same data will not change the result after the first call. When using PUT, the client specifies the exact location of the resource.

Example in C# using HttpClient:

var client = new HttpClient();

// POST - create a new resource
var postContent = new StringContent(jsonData, Encoding.UTF8, "application/json");
var postResponse = await client.PostAsync("https://api.example.com/items", postContent);

// PUT - update or create a resource at a specific URI
var putContent = new StringContent(jsonData, Encoding.UTF8, "application/json");
var putResponse = await client.PutAsync("https://api.example.com/items/123", putContent);

Thus, POST is suitable for creation, while PUT is used for updating or replacing a resource at a known address.